Many transition metals and their complexes have been used as catalysts for the formation of cyclopropanes from olefins and diazo compounds. For many years, copper compounds were favored for their combination of ready availability, low cost and acceptable reactivity with a wide range of olefins and diazo compounds. Recently, homogeneous rhodium cyclopropanation catalysts have been developed which are more active than analogous copper catalysts. Although both heterogeneous and homogeneous copper cyclopropanation catalysts are known, all of the well-known rhodium cyclopropanation catalysts are homogeneous. Improved cyclopropanation catalysts are of considerable interest to the chemical industry.
The earliest reported copper cyclopropanation catalysts were heterogeneous systems. References which are representative of this technology include: Loose, J. Prakt. Chim., 79 (2):505 (1909) which discloses copper bronze; Ebel et al., Helv. Chim. Acta, 12:19 (1926) which discloses copper powder; and Skell and Etter, Chem. Ind.(London), 6 (1958) which discloses copper sulfate. The following patents disclose heterogeneous copper compounds as cyclopropanation catalysts: U.S. Pat. No. 4,198,527 discloses Cu or CuSO.sub.4 ; U.S.S.R. Patent No. 652,172 discloses CuO; U.S.S.R. Patent No. 576,313 discloses CuO on pumice or alumina; U.S.S.R. Patent No. 4299 discloses CuSO.sub.4 on pumice, alumina, activated carbon or Cu chips; Japanese Patent No. 50,116,465 discloses Cu; DE No. 3,244,641 discloses Cu or Cu salts; and European Patent No. 22,608 discloses Cu or Cu salts.
Kirmse, Carbene Chemistry, 2nd Ed., (Academic Press, New York, N.Y., 1971) in Chapter 3, reviews both homogeneous and heterogeneous metal catalyzed decompositions of diazo-alkanes, -esters and -ketones. The use of transition metal compounds, including copper and copper salts, as cyclopropanation catalysts is described.
In a more recent review of transition metal catalyzed cyclopropanations, Catalysis of Organic Reactions, Ed. by R. L. Augustine,(M. Dekker, New York, N.Y., 1985) in Chapter 4, the author concludes that Rh(II)acetate is generally the most suitable catalyst for intermolecular cyclopropanation reactions. However, Cu(II)triflate (i.e., Cu(II)trifluoromethanesulfonate) in nitromethane is a better catalyst for intramolecular cyclopropanations.
Anciaux et al., J. Org. Chem., 45:695 (1980) disclose a comparison of several rhodium, copper and palladium cyclopropanation catalysts. With few exceptions, the relative efficiencies of three common cyclopropanation catalysts, Rh(II)acetate, Cu(II)triflate and Pd(II)acetate, were found to be Rh&gt;Cu&gt;Pd. The order of selectivity in competitive cyclopropanations is generally Rh&lt;Cu&lt;Pd.
Salomon and Kochi, J. Amer. Chem. Soc., 95:3300 (1973), show that Cu(I), not Cu(II), is probably the active catalyst species in copper-catalyzed cyclopropanations, even when the copper reagent used is nominally Cu(II), e.g. CuSO.sub.4, CuCl.sub.2, or Cu(OTf).sub.2. This disclosure is consistent with earlier observations reported by others including Komendantov et al., J. Org. Chem. U.S.S.R., 2:561 (1966), and Wittig and Schwarzenbach, Justus Lieb. Ann. Chem., 650:1 (1961).
Campbell and Harper, J. Chem. Soc., 283 (1945), disclose the synthesis of ethyl chrysanthemumates (i.e., 2,2-dimethyl-3-(2-methyl-1-propenyl)-cyclopropanecarboxylic acid ethyl esters) from the copper bronze catalyzed reaction of ethyl diazoacetate with 2,5-dimethyl-2,4-hexadiene. The use of copper catalysts in the synthesis of chrysanthemic acid esters is disclosed in the following references: Japanese Patent No. 49066660, Japanese Patent No. 54073758 and European Patent No. 128012.
Matlin et al., J. Chem. Soc., Chem. Commun., 1038 (1984), disclose a method of attaching a chiral ligand to silica, coordinating Cu(II) or Ni(II) to the immobilized chiral ligand and using this modified silica as a cyclopropanation catalyst. When the substrate olefin is styrene, the catalyst tends to become coated with polystyrene, reducing the activity of the catalyst substantially and limiting the recycle value of the catalyst. Waller, Catal. Rev. Sci. Eng., 28(1):1 (1986), reviews catalysis with metal cation-exchanged resins. U.S. Pat. No. 4,446,329 discloses the preparation of several metal salts of perfluorosulfonic acid polymers, including a Cu(II) salt obtained from the reaction of Cu(NO.sub.3).sub.2.xH.sub.2 O with the acid form of a perfluorosulfonic acid polymer. This (perfluorosulfonic acid polymer)-supported copper salt was shown to be only a slightly active catalyst for the ethylation of benzene, perhaps due to resin fusion at the reaction temperature, 240.degree. C.
Pittman, Polymer-supported Reactions in Organic Synthesis, Ed. by P. Hodge and D. C. Sherrington, (Wiley and Sons, 1980) in Chapter 5, reviews catalysis by polymer-supported transition metal complexes. The problem of metal loss due to leaching or chemical changes is disclosed.